Apparatus for transmitting mechanical vibrations



SEARCH ROOM FOR MISSING XR? M. DE VRIES 3,028,162

APPARATUS FOR TRANSMITTING MECHANICAL VIBRATIONS April 3, 1962 E T EPBIEFM Original Filed Feb. 26, 195:

f I f w, 1 M 1 3 7 INVENTOR Mac/71 6/ (/6 W765 y fvma'm'm ATTORNEYS United States Patent 3,028,162 Patented Apr. 3, 1962 free 3,028,162 APPARATUS FOR TRANSMITTING MECHANICAL 'VIBRATIONS Machiel de Vries, dc Kernpenaerstraat 51, Amsterdam, Netherlands Original application Feb. 26, 1953, Ser. No. 337,140, now Patent No. 2,825,763, dated Mar. 4, 1958. Divided and this application-Mar. 3, 1958, Ser. No. 718,598

4 Claims. (Cl. 274- 37) The present invention relates to apparatus for transmitting mechanical vibrations, and may comprise, for example, part of an acoustic device.

The invention is more particularly concerned with a gramophone pick-up, such as of the piczo-electric type, and the invention will therefore be described in connection with such devices.

In gramophone disc recording, the constant velocity principle is usually applied, i.e. a constant sound intensity is recorded on the disc with an amplitude which is inversely proportional to the frequency, so that the velocity at which the position of equilibrium is passed is constant for all frequencies. If an electromagnetic pickup is used for reproducing the record, in which pick-up the generated voltage is obtained by induction, such voltage will increase in direction proportionto the frequency, if the amplitude of the needle movement is constant.

If, however, this amplitude is not constant, but inversely proportional to the frequency, the voltage will become constant at a varying frequency. This can also be understood by bearing in mind that the induced voltage is determined by the velocity, which, in a constant velocity system, is kept constant, independently of the frequency.

If, however, the voltage is generated piezo-electrically, it is directly proportional to the amplitude. When playing a record of the type indicated above, the voltage decreases as the frequency increases, since the amplitude of the needle movement decreases as the frequency increases.

The object of this invention is to provide a coupling between the needle which follows the groove of the record and the crystal generating the piezo-electric voltage, the coupling being arranged to become closer as the frequencyincreases. in such a manner that, when the needle amplitude changes in inverse proportion to the frequency, in accordance with the constant velocity system, the piezoelectrically generated voltage remains constant, i.e. the output remains independent of the frequency.

Another object of the invention is to reduce the fragility of such transmitting apparatus, so that its mounting can therefore be effected better and more quickly.

A further object of the invention is to limit the mass of the moving parts of the apparatus as much as possible and to give said parts such a shape that natural vibrations Within the frequency range used are avoided.

According to the invention, in apparatus for transmitting mechanical vibrations, comprising at least one vibration-supplying element and a vibration-receiving element, such elements are coupled together by a coupling body of a material, with plastic properties, such as e.g. polyvinylchloride, which at low vibration frequencies behaves like a viscous mass and hence tends to damp the vibrations, but which, at high frequencies, behaves like a harder material and provides a more firm coupling between said elements.

This change of elasticity of the coupling body with the change of the frequency can be such that a perfectly horizontal voltage-frequency curve can be obtained in the audible frequency range.

For a piezo-electric pick-up, the construction can be made very simple by causing the plastic coupling body to embrace the piezo-electric crystal with a broad end and a groove or slot provided therein, While a needle, e.g.

a sapphire point, is arranged on the other, narrower end of the coupling body.

In order to enable this needle to be easily interchanged and also in order to prevent any movement of the needle in the longitudinal direction of the sound track, the needle is preferably mounted on a metallic strip, which engages in the narrower end of the coupling body by means of two lugs arranged on either side of the strip, Whereas the other end of said strip is secured e.g. to a holder for the crystal.

Movement in the longitudinal direction of the strip is prevented by this means. By deforming the strip over a portion of its length, so that, looking in the longitudinal direction of the strip, said portion is at right angles thereto, the strip becomes flexible in its own plane for permitting the needle to perform an oscillatory movement.

In apparatus of the turnover type having a coarser needle for ordinary records and a finer needle for microgroove records, this construction offers the particular advantage that the inoperative needle does not exert a disturbing influence and does not produce undesirable vibrations. This is due to its slight mass and the slight mass of the part of the coupling body connected therewith, so that no irregularities occur in the flat voltagefrequency curve.

The invention will now be described with reference to the accompanying drawing showing an embodiment of a pick-up provided with a piezo-electric crystal and with two needles, either of which as desired can be brought rapidly into the operative position by turning the apparatus through in its holder.

FIGURE 1 shows a cross-section through the apparatus, whereas FIGURE 2 shows an exploded view of the apparatus in perspective. The reference numerals designating the various parts are the same in the two figures.

Reference numeral 1 designates a crystal, one end of which is clamped between two blocks 2 and 2a. The terminals in contact with the crystal 1 are not shown.

At the other end of the crystal, a coupling body 3 is provided, which has the shape of a block of flat material as shown in FIGURE 2 and has its broadest portion provided wit-h a slot for receiving said other end of the crystal 1 therein. The coupling body 3 consists of plastic, elastically deformable material which weakly transmits low frequency vibrations, but which with increasing frequency behaves as a material that becomes firmer and firmer, so that it transmits higher frequencies more intensively. The coupling body 3 therefore causes a loose coupling at low frequencies and a more firm coupling at high frequencies between a driving needle or sapphire point 4 or 4a respectively and the crystal 1. The points or needles 4 and4a'are not directly secured to the narrower ends of the coupling body 3, but by means of an interchangeable needle holder 5 and 5a respectively.

Each needle holder 5 and 5a consists of a metallic strip having one end screwed to the associated clamping block 2 or 2a by a screw 6 or 6a, while at the other end it engages a narrow end of the coupling body 3 with two bent lugs 7 for transmitting to said body 3 vibrations directed at right angles to the longitudinal direction of the needle holder 5 or 5a and located in the plane thereof. In an opening in each needle holder 5 or 5a, the associated sapphire 4 or 4a is secured.

In order to enable the particular sapphire 4 or 4a not engaging the groove of a gramophone record being reproduced to perform an oscillatory movement, a portion of each needle holder 5 or 5a is deformed as at 8 to lie substantially at right angles to the plane of the strip, so that the needle holder 5 or 5:1 is rendered flexible about a line substantially at right angles to the plane of the strip, so that the sapphire 4 or 4a can perform an oscillatory movement in a direction normal to its axis and at right angles to the longitudinal direction of the needle holder or 5a, while undesirable movements of the sapphire 4 or 4a in the longitudinal directionv of the needle holder 5 or 5a are suppressed. The needle holder 5 or 5a reinforces the transmitting apparatus, prevents undesirable movements of the sapphire 4 or 4a and is readily interchangeable.

It will be clear that it is the great deformability of the coupling body 3 which protects the apparatus against breakage and damage, during use as well as assembly, and that the construction for connecting the needle holder and the crystal is very simple, which is of particular importance in view of the small dimensions of the parts.

It is remarkable that the voltage-frequency curve for records of the constant velocity type is perfectly fiat when the pick-up according to the invention is used and that this curve does not show any irregularities.

The coupling body 3 has the additional valuable char acteristics for use in hi-fidelity reproduction of resistance to aging, as well as thermal stability. Resistance to aging means that polyvinyl chlorides and their equivalents do not lose their desired physical properties Within the normal life of a cartridge of this type. Compare, for example, the brittleness acquired by rubber after a comparatively short time. That polyvinyl chloride is unaffected by aging is established in the Handbook of Plastics authored by Herbert R. Simonds and Carlton Ellis published by D. Van Nostrand Company, Inc., Second Printing. Thermal stability as used herein means the property of substantially retaining the physical characteristics of the material within a range of temperatures between 32 and 120 F., the range within which the pick-up is likely to be used. See Wakeman, Chemistry of Commercial Plastics published by Reinhold in 1947. Comparison of pages 321 and 540 demonstrates that rubber elongates almost ten times as much as polyvinyl chloride in range of 32 to 120 F.

This application is a division of my co-pendingap- 4 plication Serial No. 337,140, filed February 26, 1953.

This is to an appreciable extent due to the slight inert mass of the moving part of the apparatus not in use.

I claim:

1. A resilient strip stylus arm comprising a first portion in a first plane, a second portion in a plane otfset at right angles to said first plane, and a third portion in substantially the same plane as said first portion, and a stylus supported by said third portion, said first portion including integral means to detaehably mount the arm, said third portion including means to operatively engage with the driven element of a transducer means.

2. The resilient strip as defined in claim 1, wherein said third portion is provided with lugs extending angularly offset from the plane thereof.

3. In a stylus arm for use with sound reproducing transducer cartridge means, an elongated strip of thin metal having end sections extending substantially in one plane and an integral medial section extending generally in a plane normal to said one plane, One end section being provided with integrally formed means to detach- -ably mount said one section on said cartridge means,

References Cited in the file of this patent UNITED STATES PATENTS 2,752,428 Bauer Jan. 26, 1956 2,776,342 Dally Ian. 1, 1957 2,825,763 De Vries Mar. 4, 1958 

